QUANTITATIVE ESTIMATION attached to a condenser. The acids are poured in through a funnel, and a few small bits of broken unglazed pot are dropped in to prevent bumping. The acid is distilled with a moderate flame until about 70 c.c. have collected in the receiver, when the operation is stopped. The distillate is then tested for halogens by diluting largely with distilled water, and adding silver nitrate solution. The liquid should remain per- fectly clean It should also be tested for the presence of sul- phuric acid, in case it is required for sulphur estimations, by Ft FIG. 20. adding a few drops of barium chloride to a fresh portion of acid diluted as above. If pure, it is kept in a stoppered bottle. If it contains chlorine, it must be redistilled over a few crystals of silver nitrate. Fuming nitric acid has a sp. gr. of about 1*5 at 15°, boils at about 90°, and contains about 90 per cent, of HNO3. Acid of this strength can be purchased. 4. A Tube F-urnacc. — Various forms of furnace are used. Those which are heated on the principle of the Lothar Meyer hot-air furnace by a number of pin-hole gas jets are easily regulated, and can be raised to a high temperature. The Gattermann furnace, shown in the diagram (Fig. 20), is a very convenient form.